Finned tubes for use in heat exchangers

ABSTRACT

A method of manufacturing a finned tube in which fin stock is first formed as a sheath on a liner tube and the sheath is then extruded to form the fins hereon.

I Unlted States Patent 1191 1111 3,833,987 Owen I Sept. 10, 1974 1 FINNED TUBES FOR USE IN HEAT 3,144,576 8/1964 Hagmaier 72/258 x EXCHANGERS 3,184,945 5/1965 Homak et al.....

' 1 3,267,563 8/1966 [75] Inventor: Tom E. Owen, Houston, Tex. 3 2 7,5 4 3/1966 [73] Assi nee Hudson Products Cor ration 3391563 7/1968 g 3,434,323 3/1969 Houston 3,457,760 7/1969 3,503,243 3/1970 [22] F11ed. Jan. 24, 1973 fit H1972 [21] Appl. No.: 326,543 3,648,351 3/1972 Related US. Application Data FOREIGN PATENTS OR APPLICATIONS [63] Continuation of Ser. No. 114,229, Feb. 10, 1971, 374,397 6/1932 Great Britain 29/DIG. 47

abandoned. v

Primary ExaminerChar1es W. Lanham 9/ Assistant Examiner-D. C. Reiley, III

' 72/258 Attorney, Agent, or Firm-W. F. Hyer; Marvin B. [51] Int. Cl B2ld 53/02, B23p 15/26 Ei k ht [58]Field of Search ..29/157.3 A, 157.3 AH,

29/1573 B, 527.2, 527.3, DIG. 47; 57 ABSTRACT 72/2-58 A method of manufacturing a finned tube in which fin stock is first formed as a sheath on a liner tube and the [56] u lTE g gr xflis gzqr- Ts sheath is then extruded to forrn the-fins hereon. 1,101,729 6/1914 Davis 29/1510. 47 5 Clams 5 Drawmg F'gures 2,586,653 2/1952 11111 29/1575 A I-I UK/7 /&

mmsav PATENTEDSEP 1 0mm SHEET 2 BF 3 75/77 f awe/7 INVENTOR,

1 FINNED TUBES FOR USE IN HEAT EXCHANGERS This is a continuation of application, Ser. No. 1 14,229, filed Feb. 10, 1971, now abandoned.

This invention 'relates to the manufacture of finned tubes for use in heat exchangers. More particularly, in one of its aspects, this invention relates to an improved method of manufacturing finned tubes of this type in which the fins are extruded from fin stock about a liner tube. In another of its aspects, it relates to an improved finned tube made in accordance with sucha method.

The liner tube is normally a relatively hard, corrosion-resistant material, such as steel or copper, and the fin stock is normally a relatively soft, easily extrudable material, such as aluminum. In accordance with prior methods of this type,the liner tube is first inserted into a tube of the fin stock, and although it is desirable for the stock to fit the liner as closely as possible, there must be enough clearance between them to permit relative sliding between them for a length which may be thirty feet or more.

When they are assembled, the tubes are passed through a suitable machine, such as that shown and described in US. Pat. No. 2,586,653, for extruding fins of desired height and thickness from the stock. In the process of passing through the machine, the tube of fin stock is pressed tightly about the outer diameter of the tube liner. This inherently causes some longitudinal slippage between the tubes so that the mechanical bond between them is not as good as would be desired for heat exchange purposes.

Also, an effort is made to monitor the machine and program the tube lengths in such a way that there is a minimum of disparity in liner and fin stock lengths in the resulting finned tube. Despite these efforts, this method of extruding fins from the stock results in considerable wastage due to frequent overages in fin stock.

Also, of course, this prior method requires special material handling procedures, because of the need for adequate inventories of fin stock for certain sizes of finned tubes, both in length and diameter. Obviously, even if it were possible to anticipate the need for cer-. tain sizes, there is the possibility of unexpected unavailability of the fin stock for various reasons.

Still further, and as a practical matter, these tubes of fin stock are usually obtained with a temper of hardness which is a compromise between the best suited for handling and that best suited for extruding. Consequently, the fin stock is not of an optimum temper for extruding purposes.

An object of this invention is to provide a method of manufacturing finned tubes of this type which causes the fin stock to grip the tube liner with a tighter bond, and thus to provide a finned tube having better heat exchange characteristics.

Another object is to provide such a method in which there is considerably less wastage of materials, and, preferably, in which there is little or no wastage, and thus to provide a finned tube which may be manufactured less expensively. 7

Still another object is to provide such a method in which there are less materials handling problems, and, more particularly, in which there is no need to store 7 and handle tubes of fin stock of different sizes.

At least certain of these and other objects are accomplished, in accordance with the illustrated embodiments of this invention, by a method in which fin stock is extruded onto the liner tube to form a sheath thereon and the sheath is then extruded to fonn fins thereon. Thus, as compared with prior practices, wherein the fin stock is pressed onto the liner tube as fins are formed on it,'the liner tube with the fin stock thereabout is passedthrough a die opening while the stock is under pressure so as to form said sheath on the liner as the liner and fin stock pass out of the opening. As a result, the fin stock grips the liner with a tighter grip which provides a finned tube having better heat exchange characteristics. Furthermore, the grain structure of the extruded fin stock enables the extrusion of better fins from the sheath. g

More particularly, the stock is contained in bulk within a vessel having the die opening from it, and the liner tube is passed axially through the stock and out the die opening as pressure is exerted on it. The stock may be either in a molten state or a tube round in a plastic state, so that it is extruded from the die opening, as the liner tube passes through it, to thereby form the sheath thereon. Since the stock from which the sheath is formed need not be mill finished, as is necessary in the case of the tubes of fin stock used in prior practices, the resulting finned tube is less expensive. Also, the stock from which the sheath is formed may be of the hardness desired for extruding purposes since it presents no problems of handling as occurs in the case of mill finished tubes of fin stock.

In a preferred embodiment, the vessel is a die pot and the fin stock is contained within it in a molten state. This permits the manufacture of a considerably less expensive finned tube, because the stock requires no special casting. Also, since the stock is not preformed to any shape, there is less wastage of it because its length need-not be coordinated with the length of the tube liner, and it need not be inventoried and handled in large volume. That is, as compared with preformed tubes, the stock is not limited to use with particular liner tubes.

In accordance with an alternate embodiment of the invention, the fin stock is contained within a vessel as a tube round which is in a plastic state as the liner tube is passed through the hole in it. In this case, the vessel includes a means for forcing the tube round tightly onto the liner and through the die opening. This embodiment has the benefit of requiring less complicated and expensive apparatus for its practice, and therefore may be preferred in some cases.

In the drawings, wherein like reference characters are used to designate like parts:

FIG. 1 is a diagrammatic view of apparatus for use in performing the preferred method;

FIG. 2 is a diagrammatic view of somewhat modified appratus for use for performing the preferred method;

' and I of finned tubes for heat exchangers, and thus generally of a relatively hard, corrosion resistant metal, such as steel or copper. When a tube is lowered onto the rollers l 1, it is advanced from left to right for passage into and through a die pot 12 containing molten fin stock 13 by means of a plunger 14 reciprocal within a hydraulic cylinder 14a. The tubes are preferably joined in end-toend abutment so as to form in effect a continuous tube for passage through the die pot 12.

The die pot has an opening 12a in one end to receive the tube liner, and a die opening 15 in its opposite end through which the tube liner is passed out of the pot 12. Of course, the opening 12a providing an inlet to the pot would be provided with suitable seals to contain the molten fin stock therein. The die opening 15 in the opposite end of the pot is of a size sufficiently larger than the tube 10 to extrude a sheath of fin stock of desired thickness onto the tube as the tube leaves the die pot. It may be found necessary to support the tubes within the die in order to maintain them axially of the die opening, and thus insure a sheath of uniform thickness.

As in the case of the tube liner, the fin stock is of material normally used for this purpose, and thus relatively soft, easily extrudable material. However, as distinguished from prior practices, when the fin stock is provided in the form of mill finished tubes adapted to receive the tube liners, the fin stock 13 is supplied to die pot in a molten state from a melt pot 16. As indicated in FIG. 1, the fin stock melted in the pot 16 may be supplied in the form of billets 17 from a hopper 18 above the melt pot.

The head of aluminum will, of course, provide some pressure for causing the molten stock to be extruded from the die opening 15. Also, extrusion of the fin stock will be assisted by the movement of the tube liners through the die pot, although, in another sense, the pressure on the fin stock as it passes through the die opening causes the tube to move with it as it leaves the die pot. Preferably, however, the fin stock is pressured by means of a piston 19 reciprocal within a chamber 20 above and connecting with the die pot 12. The chamber 20 is separated from the melt pot 16 by a valve 21 of any suitable type for preventing the pressure exerted on the fin stock in the chamber 20 from being transmitted into the melt pot 16.

Temperature of the molten fin stock within the die pot is maintained by suitable controls at a level below that which would be detrimental to the tube liner 10. That is, the tube liner is maintained in a solid state as it passes through the molten fin stock. This is possible, of course, due to the fact that the melting point of aluminum is much lower than that of steel, for example. Preferably, the tube liner would be preheated in any suitable manner, such as by the preheater indicated at 22 in FIG. 1 to the left of opening 12a into the die pot.

The passage of the tube liners through the die pot may either be continuous or intermittent. Also, the means for advancing the tube liner may be adjustable to permit the rate at which it is passed through the die opening 15 to be controlled. Furthermore, the portion of the end wall of the die pot in which the die opening 15 is formed may be replacable by portions having die openings of other sizes to permit the extrusion of sheaths of different thicknesses about the tube liner, whereby fins of any desired height or number may subsequently be extruded from the sheath.

As the fin stock passes out the die opening 15 to form a sheath 23 about the tube liner, it changes from a molten to a plastic state, i.e., it is no longer pourable. It is important that the temperature of the sheath be controlled so as to further render the sheath solid, and thus preserve its uniform thickness. For this purpose, there is a quick chiller 24 adjacent the die opening 15 and in position to receive the sheathed tube liner as it leaves the die pot.

Additional temperature control may be required to give the sheath an optimum temper for the subsequent extruding of fins from it. For this purpose, there is a relatively long oven 25 positioned to receive the sheathed tube line from the chiller 24.

The sheathed tube lines 10 are separated into individual bi-metal tubes 26 as they leave the oven 25, and are assembled into a bank B for feeding one-by-one onto a work bench 27 of a fin extruding machine. From the work bench 27, the tubes 26 are moved through a fin extrusion head 28, such as those shown and described in US. Pat. Nos. 2,508,517, 2,508,518 and 2,562,787. As tubes 26 pass through the head 28, the sheath is extruded to form fins 29 on it and thereby complete the manufacture of a finned tube 30.

The apparatus illustrated in FIG. 2 is similar in many respects to that above described in connection with FIG. 1 and consequently many of its parts bear reference characters identical to parts in FIG. 1. However, as distinguished from the apparatus of FIG. 1, the die pot 31 of the apparatus of FIG. 2 comprises a cylinder having an annular piston 32 which may be moved longitudinally with the die pot and about the liner tubes 10, as by means of hydraulic pressure introduced into the cylinder through line 33, for applying pressure to the molten fin stock 13 as the tubes move through the die pot. Consequently, there is no need for the means for applying pressure to the stock externally of the die pot, as in the case of the chamber 20 and ram 19 of FIG. 1. Thus, in the apparatus of FIG. 2, molten fin stock passes directly from the valve 21 into the die pot 31.

As the sheathed tube liners pass through the chiller 24, they are separated and assembled into a bank C of bi-metal tubes 26 which is then placed within a tempering oven 34. As will be understood, this enables the temperature of the bi-metal tubes 26 to be controlled over a longer period of time than would normally be possible in passing the sheathed tubes through the oven 25 of FIG. 1. As indicated by the dotted lines of FIG. 2, the upper and lower ends of the oven 34 may be shifted to one side to permit the bank of bi-metal tubes to be moved into the oven and then moved out of the oven upon completion of the controlled temperature cycle.

The properly tempered bi-metal tubes are then assembled in bank D from which they are supplied oneby-one to the work bench 36 of an extruding machine. Then, as in the case of the apparatus of FIG. 1, the bimetal tubes are fed through the extruding head 37 of the machine, which may be identical to head 28, so as to extrude the sheath 23 to form fins 29 thereon.

The apparatus illustrated in FIGS. 3A, 3B and 3C includes a vessel in the form of a cylinder 40 having an open left end to receive a tube round 41 of fin stock. As in the case of the die pots 12 and 31 of FIGS. 1 and 2, the cylinder 40 has a die opening 42 in its right end which is of a size to pass tube liner with clearance, and

thus permit the extrusion of the tube round as a sheath of fin stock of desired thickness on the tube.

As indicated in FIG. 3A, a tube liner 43 is assembled above and to one side of the open left end of the vessel 40 to permit the tube round 41 to be moved from the position of FIG. 3A, wherein it is opposite the open end of the cylinder 40, into the cylinder 40. For this purpose, there is a pusher 44 which engages the left end of the tube round to move it into the cylinder, and then apply pressure thereto in a manner to be described.

As can be seen from the drawings, the tube round 41 fits relatively closely within the cylinder 40, and has a hole through it which is of a size slightly greater than that of the tube liner 43, so that when the tube round is positioned within the cylinder, the tube liner 43 may be moved easily into it. For this purpose, of course, the pusher 44 has a hole through it of substantially the same size to receive the tube liner.

The tube liner is moved through the pusher 44 and into the tube liner 41 by means of a ram 45 operated by a hydraulic cylinder 46. When the tube liner has been pushed at least a substantial distance into the tube round, the pusher 44 is caused to move from left to right, and thus to apply pressure to the tube round within the cylinder. The tube round is heated to maintain it is a plastic state within the cylinder 40, as by means of a furnace disposed about the cylinder. In any event, in this state, the fin stock will be extruded out of the die opening 42 by the pressure of pusher 44 so as to form a sheath 47 about the tube liner 43, as shown in FIG. 3C. Preferably, the portion the portion of the cylinder 40 just to the left of the die opening 42 has its outer walls tapered to provide a transition into the die opening.

As also shown in the drawings, passageways 48 are formed within a manifold 49 in which the die opening 42 is formed. Coolant may be circulated through these passageways 48 to chill the fin stock as it passes through the die opening and thereby solidify the sheath 47 on the tube as it leaves the cylinder. Thus, there may prior to being pushed'into cylinder 40. It will also be understood, of course, that a tempering oven and an extruding head would also be provided, as in the apparatus of FIGS. 1 and 2.

From the foregoing, it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the method and article.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations.

be no need for a separate chiller, as in FIGS. 1 and 2.

This is contemplated by and is within the scope of the claims.

As many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1. A method of manufacturing finned tubes for use in heat exchangers, comprising the steps of extruding fin stock onto a tube liner to form a sheath which tightly grips the tube liner, and then extruding the sheath to form fins thereon.

' 2. A method of manufacturing finned tubes for use in heat exchangers, comprising the steps of passing a liner tube having fin stock thereabout through a die while the stock is under pressure to cause the stock to be extruded from the die and thereby fonn a sheath which tightly grips said liner tube, and then extruding the sheath to form fins thereon. I

3. A method of manufacturing finned tubes for use in heat exchangers, comprising the steps of containing fin stock within a vessel having a die opening therefrom, passing a liner tube axially through the fin stock and out the die opening, exerting pressure on the fin stock to cause the stock to be extruded from the die opening as the liner tube passes through it, and thereby form a sheath of said stock which tightly grips the tube liner, and then extruding the sheath to form fins thereon.

4. A method of the character defined in claim 3, wherein the vessel is a die pot and the fin stock is contained therein in a molten state.

5. A method of the character defined in claim 2, wherein the fin stock is contained as a tube round which is in a plastic state, and the tube liner is passed through the hole in the tube round. 

1. A method of manufacturing finned tubes for use in heat exchangers, comprising the steps of extruding fin stock onto a tube liner to form a sheath which tightly grips the tube liner, and then extruding the sheath to form fins thereon.
 2. A method of manufacturing finned tubes for use in heat exchangers, comprising the steps of passing a liner tube having fin stock thereabout through a die while the stock is under pressure to cause the stock to be extruded from the die and thereby form a sheath which tightly grips said liner tube, and then extruding the sheath to form fins thereon.
 3. A method of manufacturing finned tubes for use in heat exchangers, comprising the steps of containing fin stock within a vessel having a die opening therefrom, passing a liner tube axially through the fin stock and out the die opening, exerting pressure on the fin stock to cause the stock to be extruded from the die opening as the liner tube passes through it, and thereby form a sheath of said stock which tightly grips the tube liner, and then extruding the sheath to form fins thereon.
 4. A method of the character defined in claim 3, wherein the vessel is a die pot and the fin stock is contained therein in a molten state.
 5. A method of the character defined in claim 2, wherein the fin stock is contained as a tube round which is in a plastic state, and the tube liner is passed through the hole in the tube round. 